Driving endless metal bands



A ril 21, 1970 E. D. HASENWINKLE 3,507,161

DRIVING ENDLESS METAL BANDS Filed Nov. 29, 1968 2 Sheets-Sheet 1 HE/l 75R FUEL SUPPLY 30L E/YO/D 14 TTOfP/VEYS April '2 1970 E. 0. HASENWINKLE 3,507,161

DRIVING ENDLESS METAL BANDS Filed Nov. 29, 1968 2 Sheets-Sheet 2 TEMPEK/lfl/Kf CONTROL l $2 55? 1 T FF? q I F I l HEAT J I m/vr/m 5% WATERSPRAY 4- TUNNEL $1 .a

m A GUIDE FROM W588 CONT/FOL 5/45 l/YVENTOA E/I/PL z). //43/YW//Y/YLE SOLENOID 5 U Viz/1.; 5'0 5 5? W MQ United States Patent 3,507,161 DRIVING ENDLESS METAL BANDS Earl D. Hasenwinkle, Longview, Wash., assignor to The Weyerhaeuser Company, Tacoma, Wash., a corporation of Washington Filed Nov. 29, 1968, Ser. No. 780,025

Int. Cl. F16h 7/18 US. Cl. 74241 16 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus are disclosed for driving an endless metallic band in a controlled path. According to the method, the band is rotated in one circumferential direction thereof, and a temperature differential is generated between the edge portions of the band, so as to vary the relative lengths of the portions while the band is rotating. In this way the lateral displacement of the band is controlled so as to steer it in one lateral direction thereof; or to neutralize a tendency for the band to steer in one lateral direction thereof. The temperature differential is normally initiated after the band has commenced rotating.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to endless metallic bands, and in particular to a method and apparatus for driving such bands in controlled paths. The invention is especially applicable to the driving of endless metallic bands in continuous presses, such as the presses used in laminating sheet wood material. However, it is also applicable to the driving of endless metallic bands in other situations, as for example, where such bands are employed in saws, baking ovens, and mechanical conveyors.

The problem Endless metallic bands are seldom perfect cylinders in a functional sense. Often in the course of its manufacture, a slight difference in length will develop between the edge portions of a band; or in the course of its use, internal stresses in the band will give rise to a difference in the length of its edges. Therefore, even in the absence of external forces, the band may tend to displace or steer in one lateral direction or the other, depending on which edge of the band is longer and the manner in which it is driven. Also, conversely, even a functionally stable band may tend to steer to one side or the other when subjected to external forces, as for example, in the operation of large bandsaws where the workpiece exerts considerable thrust against the band.

Description of the prior art Previously, a variety of means and techniques have been employed to compensate for the tendency of endless metallic bands to steer in one lateral direction or the other. For example, pivotally adjustable pulleys have been employed as bearings for the bands, together with a sensing device which alters the position of at least one of the pulleys until the tendency is neutralized. In addition, it has been proposed that the edges of a band should be pretensioned by heating or cold working them before the band is put to use; or that restraining forces should be sent up in a band while it is in use, to hold it in position. However, only the adjustable pulley systems have been sufficiently reliable and adaptable to win wide acceptance, and even they assume that the band will be mounted in tension and driven by means of its supports.

Objects of the invention One object of the present invention is to devise a means and technique whereby endless metallic bands can be driven in controlled paths. Another object is to devise a means and technique whereby endless metallic bands can be driven in stable rotational paths having substantially no lateral displacement; or in rotational paths having a controlled displacement in either lateral direction thereof. A further object is to devise a means and technique of this nature whereby endless metallic bands can be driven in controlled rotational paths either under tension or without tension. Other objects include the provision of a means and technique of this nature whereby such bands can be driven in controlled rotational paths without the necessity for applying restraining forces to the bands, or providing them with special supports and elaborate mechanisms for adjusting the positioning of the supports; or pretensioning them before they are used; and also a means and technique whereby such bands can be so driven with out shrinking or unduly stretching them; and without removing them from existing facilities to effect an alteration before they are returned to use. Still further objects will become aparent from a description of the invention which follows hereafter.

Summary of the invention These objects and advantages are realized by a method and apparatus of my invention wherein generally speaking, each band is rotated in one circumferential direction thereof, and a temperature differential is generated between the edge portions of the band so as to vary the relative lengths of the portions While the band is rotating. In this way the lateral displacement of the band is controlled so as to steer it in one lateral direction thereof; or to neutralize a tendency for the band to steer in one lateral direction thereof. Normally, the temperature differential is initiated afterthe band has commenced rotating. When rotation is commenced, the band may be either operationally stable or operationally unstable in a lateral sense. When an instability develops, it may be neutralized before a displacement occurs, or only after it occurs.

Moreover, the band may be rotated by a drive wheel having the band engaged thereon; or it may be rotated by a drive surface moving in engagement therewith. However, the temperature differential has an opposite effect from one situation to the other, with respect to the dimtion of displacement.

The temperature differential may be generated by either heating or cooling, or by both techniques. For example, it may be generated by heating one edge ortion of the band in relation to the other; or by cooling one in relation to the other; or by simultaneously heating one while cooling the other. Also, the differential may be generated by heating one edge portion while simultaneously cooling both portions, or by cooling one portion while simultaneously heating both. The heating or cooling effect may be generated at only one circumferential point on an edge portion; or at a number of such points up to the full cir curnference of the band.

In preferred embodiments of the invention, the differential generating means comprises means for applying heat to one edge portion of the band while it is rotating. In systems for stabilizing the band, the heat application means is normally accompanied by means for sensing a tendency for the band to undergo lateral displacement from its normal position. The signal provided by this sensory means may be observed by an operator who exercises manual control over the heat application means; or there may be additional means responsive to the signal to cause the heat application means to apply heat to the one edge portion of the band until the tendency is neutralized. Preferably, the sensory means anticipates each upcoming displacement to the extent that heat is applied to the edge portion to neutralize the tendency before any displacement actually occurs. Sensory means of this capability are known in the art.

My preferred embodiments also include means for cooling both portions of the band at a uniform rate while it is rotating, so as to assure that the band maintains a tolerable temperature throughout the operation.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the invention will be better understood by reference to the accompanying drawings wherein:

FIGURE 1 is a schematic isometric representation of an automatically controlled system in which the band is rotated by a moving drive surface in engagement therewith;

FIGURE 2 is a schematic plan representation of the band in FIGURE 1, illustrating the physical phenomenon responsible for its tendency to displace;

FIGURE 3 is a similar representation illustrating the physical phenomenon responsible for the displacement of a band rotated on a pair of parallel drive wheels;

FIGURE 4 is a schematic plan representation of a system for correcting the displacement of the band in FIGURE 3; and

FIGURE 5 is a schematic plan representation of a manually controlled system for stabilizing a band.

The band 2 shown in part in FIGURE 1 is mounted on a pair of arcuate shoes 4 disposed within the curved bights 2 thereof. Each shoe 4 comprises a pair of mutually opposing bracket plates 6 having a series of rollers 8 journalled therebetween at angularly spaced points around the rim of the shoe. The rollers provide freewheeling support for the band while it is rotated in one circumferential direction thereof. The driving force is provided by a plate surface moving lengthwise under and in frictional engagement with the lower flat 2" of the band. While in rotation the band may serve an active or a passive role. For example, it may act as a moving electrical contact for the surface 10, or it may act as a continuous slip sheet for a workpiece 10, as in the case of the slip sheet shown in the continuous laminating press of U.S. Patent No. 3,044,111 wherein the work piece is a laminar assembly of wood sheets.

As indicated hereinabove, a band such as that illustrated in FIGURE 1, cannot always be counted on to have, or to maintain dimensional uniformity. For example, during its manufacture, a slight difference in edge length may have been fabricated into the band; or during its use the band may have developed a slight difference in edge length. In either case, the band will have a slight curvature from one bight 2' to the next; and as a consequence, will not track in alignment with the plate surface 10, but instead will tend to roll or steer toward its shorter side, much as the frustum of a cone rotates about its projected point. See the schematic illustration of FIG- URE 2. wherein the band 2 has a tendency to undergo lateral displacement in the left-hand direction of the view, because it is shorter on that side. Of course, the curvature of the band is greatly exaggerated for purposes of illustrating the effect; in fact, the effect may occur even with an almost imperceptible curvature. In my experience, for example, a carbon steel band 9/64 inch shorter on one side than the other, in a total length of 675 inches, steered so sharply to that side that it virtually cut through the adjacent edge guide of a laminating press of the type illustrated in the aforementioned patent.

However, according to the invention, this tendency can be neutralized by generating a temperature differential across the width of the band, so as to vary the relative length of its edge portions. For example, by applying a hand-held propane torch to the shorter edge portion of the aforementioned 675-inch carbon steel band, it was quickly returned to a condition of alignment with the workpiece when a temperature gradient of 33 F. was generated across the width of the band. (The linear expansion for carbon steel is 6.33 10- in./in./degree F.)

A more sophisticated system which is automatically controlled is illustrated in FIGURE 1. A pilot operated gas burner 12 is mounted adjacent the bight 2' of the band so that the flame of the burner impinges on the left-hand edge portion thereof. The burner fuel is fed through a solenoid-operated gate valve 14, the solenoid of which is activated and deactivated by means of a microswitch 16 which is opened and closed by an adjustable limit control 18 arranged to straddle the bight of the band. The limit control comprises a threaded rod 20 having a pair of position contacts 22 on the ends thereof. The rod is pivotally connected to a lever 24 which actuates the microswitch, and in the operation of the system, any lateral displacement of the band which abuts it with one of the position washers 22., closes or opens the switch 16 to activate and deactivate the burner 12.

The heating effect may be discontinuous or it may be proportionate to the tendency to displace. Also, various other means such as a hot contact shoe, an electrically or gas heated conductive plate, or radiant means such as an infrared lamp, may be used to heat the band. The heat need not be applied at one point only. For example, a strip heater can be employed around the entire band.

- The temperature control illustrated by the burner 12, may be duplicated on the opposite side of the band, or the burner may be mounted on a gantry (not shown) to be applied selectively to either side. Also, a refrigerated shoe or other means for selectively cooling one of the edge portions of the band, may be substituted for the heat applicator.

In FIGURE 5 a manually controlled system for a press is illustrated, together with a water-spray tunnel 26 for maintaining the entire band at a tolerable temperature. The tunnel straddles at least one of the flats as it travels between the directional change guides (not shown) for the system. The band position detector 28 feeds its signal to a control relay 30 which is under the control in turn of the main press control (not shown), so that an operator can selectively actuate the burner 12 to furnish heat to the band 2 as necessary.

Where a band 2 is mounted on a pair of flat parallel wheels 32, as in FIGURE 3, the steering effect occasioned by a difference in edge length, is opposite. In this case, the band tends to steer toward its longer side. It is a fundamental law of belting that a band or other belt must approach a pulley in a direction perpendicular to the pnlleys axis if the belt is to stay on the pulley. Consider the point T on the band 2 in FIGURE 3. The band is curved with its shorter side on the left, and as the point T touches the lower wheel 32 the functional forces of the aforementioned law tend to drive it circumferentially to point C rather than to point T. Thus, even though all points T on the band appear to run to the left of the view, the band as a whole tends to steer to the right of the view.

By applying a temperature gradient across the band, it is possible to achieve a stable condition. Assume that heat is applied to the shorter or left hand side of the band (or that a cooling eifect is generated on the right hand side). As the heat is applied, the band becomes a more perfect cylinder functionally speaking, and now tends to approach the wheel in a direction perpendicular to its axis. Given sufficient heat, a stable condition is achieved; and with a greater degree of heat, the band in fact, can be made to steer to the other side, that is, to the left, toward the heat.

It is well known, of course, that a rotating band such as that shown at 2 in FIGURE 3, can be laterally controlled by canting the axis of each wheel 32 to the band, as illustrated in FIGURE 4. However, the band remains unstable in the sense of being readily displaceable in one lateral direction or the other, and especially in the direction of its longer side. According to the invention, this lateral instability can be used to advantage, for example, to offset an external thrust on the band as in the operation of large bandsaws, or to achieve a positive displacement of the band for cutting purposes. During the cutting operation, the portion of the toothed edge of the saw between the wood and the driving Wheel is stretched, thus causing the band to contact the wheel out of perpendicular. This in turn results in a thrust against the body of the wood, either as a counterthrust to the feed of the same, or as the driving force to feed the saw through the wood.

FIGURE 4 also illustrates a system of coordinated temperature controls 34, either for heating or cooling the edge portions of the band, or both. The controls are coordinated by a heat control 36 which is responsive to a position detector 28.

In all cases of stabilizing a band, care should be taken to keep the temperature of the band well below the yield point, since if the temperature exceeds this point the band will shrink on cooling, thus exaggerating the tendency to displace.

What is claimed is:

1. A method of driving an endless metallic band in a controlled path, comprising rotating the band in one circumferential direction thereof, and generating a temperature dilferential between the edge portions of the band so as to vary the relative lengths of the portions while the band is rotating.

2. The method according to claim 1 wherein the relative lengths of the portions are varied so as to neutralize a tendency for the band to steer in one lateral direction thereof.

3. The method according to claim 1 wherein the relative lengths of the portions are varied so as to steer the band in one lateral direction thereof.

4. The method according to claim 1 wherein the temperature differential is initiated after the band has commenced rotating.

5. The method according to claim 1 wherein the band is rotated by a drive wheel having the band engaged thereon.

6. The method according to claim 1 wherein the band is rotated by a drive surface moving in engagement therewith.

7. The method according to claim 1 wherein the temperature differential is generated by heating one edge portion of the band in relation to the other.

8. The method according to claim 1 wherein the temperature differential is generated by cooling one edge portion of the band in relation to the other.

9. The method according to claim 1 wherein the temperature differential is generated by simultaneously heating one edge portion of the band while cooling the other. 10. The method according to claim 1 wherein the temperature differential is generated by heating one edge portion of the band while simultaneously cooling both edge portions thereof.

11. In apparatus for rotating an endless metallic band in one circumferential direction thereof, means for generating a temperature differential between the edge portions of the band, so as to vary the relative lengths of the portions while the band is rotating.

12. Apparatus according to claim 11 wherein the differential generating means include means for applying heat to one edge portion of the band while it is rotating.

13. Apparatus according to claim 12 further comprising means for sensing a tendency for the band to undergo lateral displacement from the normal position thereof.

14. Apparatus according to claim 13 further comprising means responsive to a signal from the sensory means to cause the heat application means to heat the one edge portion of the band until the tendency is neutralized.

15. Apparatus according to claim 12 further comprising means for cooling both edge portions of the band at a uniform rate while it is rotating.

16. In apparatus for rotating an endless metallic band in one circumferential direction thereof, means responsive to a lateral displacement of the band from the normal position thereof, to generate a temperature differential JAMES A. WONG, Primary Examiner 

